Systems and methods for annealing semiconductor structures

ABSTRACT

Systems and methods are provided for annealing a semiconductor structure. In one embodiment, the method includes providing an energy-converting structure proximate a semiconductor structure, the energy-converting structure comprising a material having a loss tangent larger than that of the semiconductor structure; providing a heat reflecting structure between the semiconductor structure and the energy-converting structure; and providing microwave radiation to the energy-converting structure and the semiconductor structure. The semiconductor structure may include at least one material selected from the group consisting of boron-doped silicon germanium, silicon phosphide, titanium, nickel, silicon nitride, silicon dioxide, silicon carbide, n-type doped silicon, and aluminum capped silicon carbide. The heat reflecting structure may include a material substantially transparent to microwave radiation and having substantial reflectivity with respect to infrared radiation.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S.application Ser. No. 16/048,847, filed Jul. 30, 2018, which is acontinuation application of U.S. application Ser. No. 15/639,055, filedJun. 30, 2017, now U.S. Pat. No. 10,037,906, which is a continuationapplication of U.S. application Ser. No. 15/234,076, filed Aug. 11,2016, now U.S. Pat. No. 9,698,026, which is a continuation applicationof U.S. application Ser. No. 14/819,536, filed Aug. 6, 2015, now U.S.Pat. No. 9,418,871, which is a continuation application of U.S.application Ser. No. 14/066,756, filed Oct. 30, 2013, now U.S. Pat. No.9,129,918, each of which is hereby incorporated by reference in itsentirety.

FIELD

The technology described in this patent document relates generally tosemiconductor materials and more particularly to processing ofsemiconductor materials.

BACKGROUND

Modern semiconductor devices are often fabricated through manyprocesses. For example, a semiconductor substrate for device fabricationmay be doped (e.g., adding desired impurities into the substrate) toform junctions. Dopants introduced into the substrate are usuallyelectrically activated before semiconductor devices can be fabricated onthe substrate. The activation of the dopants often includes transferringthe dopant atoms/molecules from interstitial positions into latticesites of the lattice structure of the substrate. Different annealingtechniques may be used for dopant activation, such as rapid thermalannealing (RTA), and laser annealing.

Under certain circumstances, the fabrication process of semiconductordevices involves microwave radiation which typically includeselectromagnetic waves with wavelengths ranging from 1 m to 1 mm(corresponding to frequencies between 0.3 and 300 GHz). When microwaveradiation is applied to a certain material (e.g., a dielectric material)which includes electric dipoles, the dipoles change their orientationsin response to the changing electric fields of the microwave radiationand thus the material may absorb the microwave radiation to generateheat. The response of the material to the electric field of themicrowave radiation can be measured using a complex permittivity, ε(ω)*,which depends on the frequency of the electric field:ε(ω)*=ε(ω)′iε(ω)″=ε₀(ε_(r)(ω)′iε _(r)(ω)″)  (1)where ω represents the frequency of the electric field, ε(ω)′ representsa real component of the complex permittivity (i.e., a dielectricconstant), and ε(ω)″ represents a dielectric loss factor. In addition,ε₀ represents the permittivity of a vacuum, ε_(r)(ω)′ represents therelative dielectric constant, and ε_(r)(ω)″ represents the relativedielectric loss factor.

Whether a material can absorb the microwave radiation can becharacterized using a loss tangent, tan δ:

$\begin{matrix}{{\tan\;\delta} = \frac{{ɛ^{''}\mu^{\prime}} - {ɛ^{\prime}\mu^{''}}}{{ɛ^{\prime}\mu^{\prime}} + {ɛ^{''}\mu^{''}}}} & (2)\end{matrix}$where μ′ represents a real component of the magnetic permeability of thematerial, and μ″ represents a magnetic loss factor. Assuming negligiblemagnetic loss (i.e., μ″=0), the loss tangent of a material is expressedas follows:

$\begin{matrix}{{\tan\;\delta} = {\frac{ɛ^{''}}{ɛ^{\prime}} = \frac{ɛ_{r}^{''}}{ɛ_{r}^{\prime}}}} & (3)\end{matrix}$

Materials with a low loss tangent (e.g., tan δ<0.01) allow microwaves topass through with very little absorption. Materials with an extremelyhigh loss tangent (e.g., tan δ>10) reflect microwaves with littleabsorption. Materials with an intermediate loss tangent (e.g., 10≥tanδ≥0.01) can absorb microwave radiation.

SUMMARY

In accordance with the teachings described herein, systems and methodsare provided for annealing a semiconductor structure. For example, asemiconductor structure is provided. An energy-converting structurecapable of increasing the semiconductor structure's absorption ofmicrowave radiation is provided. A heat reflecting structure is providedbetween the energy-converting structure and the semiconductor structure,the heat reflecting structure being capable of reflecting thermalradiation from the semiconductor structure. Microwave radiation isapplied to the energy-converting structure and the semiconductorstructure to anneal the semiconductor structure for fabricatingsemiconductor devices.

In one embodiment, a system for annealing a semiconductor structureincludes an energy-converting structure, a heat reflecting structure,and a microwave-radiation source. The energy-converting structure isconfigured to increase a semiconductor structure's absorption ofmicrowave radiation. The heat reflecting structure is configured toreflect thermal radiation from the semiconductor structure, the heatreflecting structure being disposed between the energy-convertingstructure and the semiconductor structure. The microwave-radiationsource is configured to apply microwave radiation to theenergy-converting structure and the semiconductor structure to annealthe semiconductor structure for fabricating semiconductor devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an example diagram for annealing a semiconductorstructure using microwave radiation.

FIG. 2 depicts another example diagram for annealing a semiconductorstructure using microwave radiation.

FIG. 3 depicts yet another example diagram for annealing a semiconductorstructure using microwave radiation.

FIG. 4 depicts another example diagram for annealing a semiconductorstructure using microwave radiation.

FIG. 5 depicts an example diagram showing a system for annealing asemiconductor structure using microwave radiation.

FIG. 6 depicts an example diagram showing a flow chart for annealing asemiconductor structure using microwave radiation.

DETAILED DESCRIPTION

The conventional annealing technologies often have some disadvantages.For example, a substrate used for device fabrication often includesvarious device patterns (e.g., through deposition, lithography and/oretching). These different patterns usually correspond to differentthicknesses and material types which result in different heatemissivity. During an annealing process (e.g., RTA), different regionson the substrate often absorb and emit different amounts of heat, whichresults in localized temperature non-uniformity on the substrate.Furthermore, photons of light sources (e.g., lamps used for RTA orlasers used for laser annealing) may not penetrate beyond surfaceregions of the substrate, which often causes uneven heating of thesubstrate at different depths.

FIG. 1 depicts an example diagram for annealing a semiconductorstructure using microwave radiation. As shown in FIG. 1, microwaveradiation is applied to an energy-converting structure (e.g., made ofenergy converting material) 102 and a semiconductor structure 104 toanneal the semiconductor structure 104 (e.g., for dopant activation). Aheat reflecting structure 106 is disposed between the energy-convertingstructure 102 and the semiconductor structure 104 to reflect thermalradiation back to the semiconductor structure 104 during the annealingprocess. Microwave radiation penetrates deeply into the semiconductorstructure 104 and results in volumetric heating of the semiconductorstructure 104.

Specifically, the semiconductor structure 104 which has a small losstangent may not absorb microwave radiation efficiently. Theenergy-converting structure 102 which has a large loss tangent (e.g., ina range of about 0.01 to about 2) absorbs microwave radiation moreefficiently, and in response a temperature associated with theenergy-converting structure 102 increases rapidly. On one hand, the heatgenerated by the energy-converting structure 102 may increase thetemperature of the semiconductor structure 104 (e.g., through conductionor radiation). At the elevated temperature, the interaction between thesemiconductor structure 104 and the microwave radiation increases. Onthe other hand, the energy-converting structure 102 increases anelectric field density over the semiconductor structure 104 (e.g., thetemperature of the semiconductor structure 104 being raised to 400°C.-700° C.). For example, at the raised electric field density, theelectric field reacts with defects within the semiconductor structure104 through interfacial polarization so as to further activate thedopants.

During the annealing process, the semiconductor structure 104 emitsthermal radiation (e.g., infrared radiation). The heated heat reflectingstructure 106 reflects such thermal radiation back to the semiconductorstructure 104 so that the thermal radiation generated by thesemiconductor structure 104 is conserved between the heat reflectingstructure 106 and the semiconductor structure 104 (e.g., to reducelocalized temperature non-uniformity). The distance (e.g., d1) betweenthe heat reflecting structure 106 and the semiconductor structure 104may be adjusted to ensure that most thermal radiation from thesemiconductor structure 104 is reflected back. In certain embodiments,the heat reflecting structure 106 is placed on top of device patternsformed on the semiconductor structure 104. For example, the heatreflecting structure 106 is approximately transparent to the microwaveradiation, and is opaque to the thermal radiation (e.g., infraredradiation). As an example, the heat reflecting structure 106 has areflectivity larger than 95% with respect to infrared radiation. In someembodiments, the heat reflecting structure 106 includes a semiconductorwafer (e.g., a blank silicon wafer) that contains dopants to provideadditional free carriers. In certain embodiments, the heat reflectingstructure 106 includes a semiconductor wafer (e.g., a blank siliconwafer) that does not contain dopants.

For example, the semiconductor structure 104 includes a junction with anumber of dopants formed on a substrate at an elevated temperature(e.g., in a range of about 300° C. to about 600° C.) by epitaxialgrowth. The microwave radiation is applied to anneal the semiconductorstructure 104 for dopant activation. The energy-converting structure 102intensifies the electric field density over the semiconductor structure104. The semiconductor structure 104 absorbs more microwave radiationunder the increased electric field density. More and more reactionsbetween the electric field and defects in the semiconductor structure104 occur through interfacial polarization. For example, positivecharges and/or negative charges accumulated at boundaries of the defectsmay cause the defects to dissolve eventually for further dopantactivation. Once the electric field density over the semiconductorstructure 104 exceeds a threshold, the interfacial polarizationeventually breaks the bonds between the dopants and the interstitialsites in the semiconductor structure 104, so that the dopants areactivated. The distance (e.g., d2) between the energy-convertingstructure 102 and the semiconductor structure 104 may be adjusted toimprove the dopant activation. For example, the dopants includephosphorous, phosphorous-based molecules, germanium, helium, boron,boron-based molecules, or other materials.

In some embodiments, the microwave radiation applied to theenergy-converting structure 102 has a frequency in the range of about 2GHz to about 10 GHz. For example, the energy-converting structure 102includes boron-doped silicon germanium, silicon phosphide, titanium,nickel, silicon nitride, silicon dioxide, silicon carbide, n-type dopedsilicon, aluminum cap silicon carbide, or other materials. Theenergy-converting structure 102 may have a larger size than thesemiconductor structure 104 so that the electric field density may beapproximately uniform over the semiconductor structure 104. In certainembodiments, the temperature of the semiconductor structure 104 is keptwithin a range of about 300° C. to about 600° C. to reduce dopantdiffusion. For example, the microwave radiation is applied to theenergy-converting structure 102 and the semiconductor structure 104 fora time period within a range of about 40 seconds to about 300 seconds.

FIG. 2 depicts another example diagram for annealing a semiconductorstructure using microwave radiation. As shown in FIG. 2, microwaveradiation is applied to an energy-converting structure 202 and asemiconductor structure 204 to anneal the semiconductor structure 204(e.g., for dopant activation). A heat reflecting structure 206 is formedon the energy-converting structure 202 and is disposed on top of thesemiconductor structure 204 to reflect thermal radiation back to thesemiconductor structure 204 during the annealing process. For example,the heat reflecting structure 206 is formed on the energy-convertingstructure 202 through epitaxial growth, (e.g., deposition). As anexample, the energy-converting structure 202 is capable of generatingthe thermal radiation in response to the applied microwave radiation andincreasing an electric field density over the semiconductor structure204.

During the annealing process, the heat reflecting structure 206 reflectsthermal radiation emitted by the semiconductor structure 204 back to thesemiconductor structure 204 so that such thermal radiation is conservedbetween the heat reflecting structure 206 and the semiconductorstructure 204 (e.g., to reduce localized temperature non-uniformity).For example, the heat reflecting structure 206 (e.g., a blank siliconwafer) is approximately transparent to the microwave radiation andopaque to the thermal radiation (e.g., infrared radiation).

FIG. 3 depicts yet another example diagram for annealing a semiconductorstructure using microwave radiation. As shown in FIG. 3, microwaveradiation is applied to two energy-converting structures 302 and 308 anda semiconductor structure 304 to anneal the semiconductor structure 304(e.g., for dopant activation). A heat reflecting structure 306 isdisposed between the energy-converting structure 302 and thesemiconductor structure 304 to reflect thermal radiation back to thesemiconductor structure 304 during the annealing process.

For example, the energy-converting structures 302 and 308 have a sameloss tangent or different loss tangents. As an example, the distance(e.g., d1) between the energy-converting structure 302 and thesemiconductor structure 304 is the same as or different from thedistance (e.g., d2) between the energy-converting structure 308 and thesemiconductor structure 304. In some embodiments, the heat reflectingstructure 306 is formed on the energy-converting structure 302 throughepitaxial growth, (e.g., deposition), as shown in FIG. 4.

FIG. 5 depicts an example diagram showing a system for annealing asemiconductor structure using microwave radiation. As shown in FIG. 5, ashell 502 includes a microwave port 504 through which microwaveradiation may be introduced into the shell 502. During the annealingprocess, microwave radiation generated by a microwave-radiation source512 is applied to an energy-converting structure 506 and a semiconductorstructure 510 to anneal the semiconductor structure 510 (e.g., fordopant activation). A heat reflecting structure 508 is disposed betweenthe energy-converting structure 506 and the semiconductor structure 510to reflect thermal radiation back to the semiconductor structure 510.For example, the shell 502 is made of a metal material. As an example,the energy-converting structure 506 is pre-heated to a predeterminedtemperature (e.g., in a range of about 300° C. to about 600° C.) by aheat source (e.g., an Ar lamp, a Xeon lamp, or a tungsten-halogen lamp).

In some embodiments, an additional energy-converting structure is placedin the shell 502 so that the semiconductor structure 510 is disposedbetween the heat reflecting structure 508 and the additionalenergy-converting structure. In certain embodiments, the heat reflectingstructure 508 is formed on the energy-converting structure 506 throughepitaxial growth.

FIG. 6 depicts an example diagram showing a flow chart for annealing asemiconductor structure using microwave radiation. At 602, asemiconductor structure is provided. For example, the semiconductorstructure includes a plurality of dopants. At 604, an energy-convertingstructure capable of increasing the semiconductor structure's absorptionof microwave radiation is provided. For example, the energy-convertingstructure is capable of increasing an electric field density associatedwith the semiconductor structure. As an example, the energy-convertingstructure includes boron-doped silicon germanium, silicon phosphide,titanium, nickel, silicon nitride, silicon dioxide, silicon carbide, orother materials.

At 606, a heat reflecting structure is disposed between theenergy-converting structure and the semiconductor structure. The heatreflecting structure is capable of reflecting thermal radiation from thesemiconductor structure. For example, the heat reflecting structureincludes a blank silicon wafer. The thermal radiation includes infraredradiation. In some embodiments, the heat reflecting structure has areflectivity larger than 95% with respect to infrared radiation, and isapproximately transparent to the microwave radiation.

At 608, microwave radiation is applied to the energy-convertingstructure and the semiconductor structure to anneal the semiconductorstructure (e.g., for dopant activation). For example, theenergy-converting structure increases the electric field density inresponse to the microwave radiation so as to affect dipoles formed inthe semiconductor structure and motions of the formed dipoles. Theformed dipoles are related to dopants in the semiconductor structure. Asan example, the semiconductor structure's absorption of microwaveradiation is increased in response to the increased electric fielddensity so as to dissolve certain dopant clusters included in thesemiconductor structure.

Accordingly, one aspect of the instant disclosure provides a method thatcomprises: providing an energy-converting structure proximate asemiconductor structure, the energy-converting structure comprising amaterial having a loss tangent larger than that of the semiconductorstructure; providing a heat reflecting structure between thesemiconductor structure and the energy-converting structure; andproviding microwave radiation to the energy-converting structure and thesemiconductor structure.

Accordingly, another aspect of the instant disclosure provides a systemfor annealing a semiconductor structure, the system comprises: a firstenergy-converting structure arranged proximate the semiconductorstructure to be annealed, comprising a material having a loss tangentlarger than that of the semiconductor structure; a heat reflectingstructure arranged between the semiconductor structure and the firstenergy-converting structure; and a microwave source for generatingmicrowave radiation to anneal the semiconductor structure.

Accordingly, yet another aspect of the instant disclosure provides amethod of annealing a semiconductor structure using a microwave system,the method comprises: arranging an energy-converting structure proximatethe semiconductor structure, the semiconductor structure comprising atleast one material selected from the group consisting of boron-dopedsilicon germanium, silicon phosphide, titanium, nickel, silicon nitride,silicon dioxide, silicon carbide, n-type doped silicon, and aluminumcapped silicon carbide; arranging a heat reflecting structure betweenthe semiconductor structure and the energy-converting structure, theheat reflecting structure comprising a material substantiallytransparent to microwave radiation and having substantial reflectivitywith respect to infrared radiation; and generating microwave radiationwith a microwave source to anneal the semiconductor structure.

This written description uses examples to disclose embodiments of thedisclosure, include the best mode, and also to enable a person ofordinary skill in the art to make and use various embodiments of thedisclosure. The patentable scope of the disclosure may include otherexamples that occur to those of ordinary skill in the art. One ofordinary skill in the relevant art will recognize that the variousembodiments may be practiced without one or more of the specificdetails, or with other replacement and/or additional methods, materials,or components. Further, persons of ordinary skill in the art willrecognize various equivalent combinations and substitutions for variouscomponents shown in the figures.

Well-known structures, materials, or operations may not be shown ordescribed in detail to avoid obscuring aspects of various embodiments ofthe disclosure. Various embodiments shown in the figures areillustrative example representations and are not necessarily drawn toscale. Particular features, structures, materials, or characteristicsmay be combined in any suitable manner in one or more embodiments. Thepresent disclosure may repeat reference numerals and/or letters in thevarious examples, and this repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed. Various additionallayers and/or structures may be included and/or described features maybe omitted in other embodiments. Various operations may be described asmultiple discrete operations in turn, in a manner that is most helpfulin understanding the disclosure. However, the order of descriptionshould not be construed as to imply that these operations arenecessarily order dependent. In particular, these operations need not beperformed in the order of presentation. Operations described herein maybe performed in a different order, in series or in parallel, than thedescribed embodiments. Various additional operations may be performedand/or described. Operations may be omitted in additional embodiments.

This written description and the following claims may include terms,such as top, on, over, etc. that are used for descriptive purposes onlyand are not to be construed as limiting. The embodiments of a device orarticle described herein can be manufactured, used, or shipped in anumber of positions and orientations. For example, terms designatingrelative vertical position may refer to a situation where a device side(or active surface) of a substrate or integrated circuit is the “top”surface of that substrate; the substrate may actually be in anyorientation so that a “top” side of a substrate may be lower than the“bottom” side in a standard terrestrial frame of reference and may stillfall within the meaning of the term “top.” The term “on” or “over” asused herein (including in the claims) may not necessarily indicate thata first layer/structure “on” or “over” a second layer/structure isdirectly on or over and in immediate contact with the secondlayer/structure unless such is specifically stated; there may be one ormore third layers/structures between the first layer/structure and thesecond layer/structure. The term “substrate” used herein (including inthe claims) may refer to any construction comprising one or moresemiconductive materials, including, but not limited to, bulksemiconductive materials such as a semiconductive wafer (either alone orin assemblies comprising other materials thereon), and semiconductivematerial layers (either alone or in assemblies comprising othermaterials). The term “semiconductor structure” used herein (including inthe claims) may refer to shallow trench isolation features, poly-silicongates, lightly doped drain regions, doped wells, contacts, vias, metallines, or other types of circuit patterns or features to be formed on asemiconductor substrate. In addition, the term “semiconductor structure”used herein (including in the claims) may refer to various semiconductordevices, including transistors, capacitors, diodes, and other electronicdevices that obey semiconductor physics and/or quantum mechanics.

What is claimed is:
 1. A system comprising: a radiation source forgenerating first radiation; a shell defining an interior cavity, whereinthe shell includes an opening through which the first radiationgenerated by the radiation source passes through; a semiconductorstructure disposed within the interior cavity of the shell; anenergy-converting structure disposed within the interior cavity of theshell, the energy-converting structure configured to convert firstradiation into second radiation; and a second radiation reflectingstructure disposed within the interior cavity of the shell, wherein thesecond radiation reflecting structure reflects second radiationgenerated by the semiconductor structure back towards the semiconductorstructure.
 2. The system of claim 1, wherein the second radiationreflecting structure is disposed over the semiconductor structure andthe energy-converting structure is disposed over the second radiationreflecting structure.
 3. The system of claim 2, wherein theenergy-converting structure is spaced apart from the second radiationreflecting structure.
 4. The system of claim 1, wherein the firstradiation includes microwave radiation and the second radiation includesthermal radiation.
 5. The system of claim 1, wherein the shell includesonly the single opening through which the first radiation generated bythe radiation source passes through.
 6. The system of claim 1, whereinthe second radiation reflecting structure includes a semiconductorwafer.
 7. The system of claim 1, wherein the shell is formed of a metalmaterial.
 8. A system comprising: a radiation source for generatingfirst radiation; an energy-converting structure disposed over asemiconductor structure, the energy-converting structure configured toconvert first radiation into second radiation; and a semiconductor waferpositioned between the semiconductor structure and the energy-convertingstructure, wherein the semiconductor wafer reflects second radiationgenerated by the semiconductor structure back towards the semiconductorstructure, wherein the semiconductor wafer is spaced apart from theenergy-converting structure and the semiconductor structure.
 9. Thesystem of claim 8, wherein the semiconductor wafer is positioned a firstdistance away from the energy-converting structure and a second distanceaway from the semiconductor wafer, the first distance being the same asthe second distance.
 10. The system of claim 8, wherein thesemiconductor wafer is positioned a first distance away from theenergy-converting structure and a second distance away from thesemiconductor wafer, the first distance being different than the seconddistance.
 11. The system of claim 8, further comprising anotherenergy-converting structure disposed under the semiconductor structure.12. The system of claim 11, wherein the another energy-convertingstructure is spaced apart from the semiconductor structure.
 13. Thesystem of claim 8, wherein the radiation source is a microwave radiationsource, wherein the energy-converting structure is configured to convertmicrowave radiation into thermal radiation, and wherein thesemiconductor wafer reflects thermal radiation generated by thesemiconductor structure back towards the semiconductor structure. 14.The system of claim 8, wherein the energy-converting structure includesat least one material selected from the group consisting of boron-dopedsilicon germanium, silicon phosphide, titanium, nickel, silicon nitride,silicon dioxide, silicon carbide, n-type doped silicon, and aluminum capsilicon carbide.
 15. A method comprising: providing a firstenergy-converting structure and a thermal radiation reflecting structureproximate a semiconductor structure; adjusting one of the thermalradiation reflecting structure and the semiconductor structure to changea distance between the thermal radiation reflecting structure and thesemiconductor structure; and providing radiation to the firstenergy-converting structure while the thermal radiation reflectingstructure is between the semiconductor structure and the firstenergy-converting structure.
 16. The method of claim 15, wherein thethermal radiation reflecting structure is spaced apart from the firstenergy-converting structure during the providing of the radiation to thefirst energy-converting structure while the thermal radiation reflectingstructure is between the semiconductor structure and the firstenergy-converting structure.
 17. The method of claim 15, furthercomprising epitaxially growing the thermal radiation reflectingstructure on the first energy-converting structure.
 18. The method ofclaim 15, further comprising positioning the first energy-convertingstructure, the thermal radiation reflecting structure and thesemiconductor structure into an interior cavity of a shell, and whereinthe providing of the radiation to the first energy-converting structureincludes proving the radiation through an opening in the shell to thefirst energy-converting structure disposed within the cavity of theshell.
 19. The method of claim 15, wherein the providing of theradiation to the first energy-converting structure includes applyingradiation to the semiconductor structure to activate a dopant region onthe semiconductor structure.
 20. The method of claim 15, wherein thethermal radiation reflecting structure includes a silicon wafer.